The FIR was registered on a complaint received at the anti-corruption helpline 1031 and the accused inspector has been identified as Rajkumari, who is posted at Dwarka North police station.
Preliminary inquiry revealed that Rajkumari was probing the murder case of complainant's husband.
"She had been demanding money from the complainant and threatening to implicate and arrest her in the murder case," Surender Singh Yadav, Additional Commissioner of Police (ACB), said in statement.
The inspector, initially, demanded Rs 2 lakh from the complainant but later settled for an amount of Rs 75,000 after negotiations, Yadav said.